Formation and maintenance of community boundaries in a sub-alpine forest landscape in northern Japan

We focused on community boundaries in a sub-alpine forest landscape in the Shiretoko Peninsula, northern Japan. Gradient-directed transects were conducted on the northwestern slope (ranging 500-600 m a.s.l.) of Mount On'nebetsu (1331 m), where complex topography was formed by past landslides. Pioneer Picea glehnii made up a mosaic of pure stands related to landslides. Structural and compositional changes from P. glehnii pure stands to P. glehnii and Abies sachalinensis mixed stands were characterized by ca. 20 m transitional zones over the landscape. Stand density of the species changed across boundaries. A. sachalinensis preferred less undulated slopes with deep soil and P. glehnii preferred undulated rocky sites. Positive spatial associations between overstorey-understorey P. glehnii were found at undulated core parts of P. glehnii pure stands. Short-lived A. sachalinensis grew faster to the smaller maximum size than long-lived P. glehnii. Undulated topography controlled the increase of A. sachalinensis and provided regeneration sites for P. glehnii, which prevented the general trend of canopy replacement from P. glehnii to late-successional A. sachalinensis. However, the locations of current boundaries were not accordant with the topographic changes in the meso-scale landscape. Initial P. glehnii pure stands would extend to larger areas if Current patterns reflect vegetation recovery since the last landslide. P. glehnii pure stands with accurate boundaries were not maintained by topographic complexity, but were dynamically arranged by the one-sided canopy replacements from P. glehnii to A. sachalinensis at less undulated slopes in the sub-alpine forest landscape.